ozandincel
Bioengineer
I am looking for to learn more about the mechanical properties of comparison of casting and forging method.
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Machanical properties of casting and forging 1
- Thread starter ozandincel
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EnglishMuffin
Mechanical
All metal objects start out as castings at some point. They may or may not have additional processes applied to them, one of which is forging. So forging modifies to some extent the properties of the original casting. During forging, the coarse "as-cast" grain structure is broken down and replaced by one of relatively fine grain. At the same time, impurities are redistributed in a more or less fibrous form. It is therefore more advantageous from a strength point of view, all other things being equal, to attain the final form of a component by forging rather than producing it "as-cast". It is usually the case that the "grain-flow" of a forging closely follows the finished contours, which is generally regarded as being beneficial from the standpoint of fatigue strength.
JimMetalsCeramics
Materials
Forging induces a great deal of plastic strain within a metal. This generally increases a material's hardness and plastic yield strength, in particular at its surfaces. If too much strain is induced, cracking may occur. Short of cracking, one may overstress the part, even on purpose, and then back-temper. This means to heat the part to relieve some of the strain and equilibrate it (at least a little) throughout the material. Parts made through powder metallurgy means (not cast) are also often forged.
EnglishMuffin
Mechanical
OK - I suppose I should have said all solid metals start out as castings at some point - even the grains of metal powder used in powder metallurgy are tiny castings, and suffer from the limitations of a cast structure until further processed.
EnglishMuffin
Mechanical
Actually - having checked up, I'm not going to win this one - at least some powders are produced by electrolysis rather than atomisation and solidification.
JimMetalsCeramics
Materials
Many powders are also ground, some are precipitated, many are milled. Nanopowders are made through a slew of other processes (e. g., CVD).
EnglishMuffin
Mechanical
OK - looks like I should have said "most metals start out as castings at some point".
Depending on the material, there can be a great difference between cast and forged materials.
Both techniques are developed to get a near net shaped part, but that is where the similarity ends.
A very common analogy is the bread dough. If you just mix the bread flour and water, and bake it, the bread is very brittle and crummbles easily.
On the other hand, if you knead the dough for a long time, you end up with a chewy bread.
The forged parts will usually have a better mechanical properties such as strength, fatigue properties etc. It will also be lower on porosity, inclusions etc.
The other problem with cast structure is something called as "coring" or "segregation". In addition, in case of castings, there is a very distinct property gradient. The dendrites have different properties and chemistry as compared to the interdendritic regions.
Some of these can be eliminated by heat treament and modified casting processes such as pressure die casting and use of chilling.
Even with this, in most cases, the forged part will be considerably better when compared to a cast part.
Both techniques are developed to get a near net shaped part, but that is where the similarity ends.
A very common analogy is the bread dough. If you just mix the bread flour and water, and bake it, the bread is very brittle and crummbles easily.
On the other hand, if you knead the dough for a long time, you end up with a chewy bread.
The forged parts will usually have a better mechanical properties such as strength, fatigue properties etc. It will also be lower on porosity, inclusions etc.
The other problem with cast structure is something called as "coring" or "segregation". In addition, in case of castings, there is a very distinct property gradient. The dendrites have different properties and chemistry as compared to the interdendritic regions.
Some of these can be eliminated by heat treament and modified casting processes such as pressure die casting and use of chilling.
Even with this, in most cases, the forged part will be considerably better when compared to a cast part.
foundrymaninchina
Mechanical
the squeeze aluminum castings have almost the same mechanical properties as forgings.
priyasachin
Materials
Dear Friend,
Somuch on the benefits of forging over casting. One point to note is the aspect of anisotrophy, the differences in the properties in the direction of forming and across. In perticular, the ductility properties viz. reduction in area, which is affected significantly. Whereas the casting has no anisotrophy at all, forging is a prisoner to this effect. This level of anisotrophy is dependent on the type and the level of impurity, the extent of working.
If one has to deal with HIC resistance, if the product is a casting there is cosiderable less problem, than what is called for a wrought product.
Regards,
MRCN
Somuch on the benefits of forging over casting. One point to note is the aspect of anisotrophy, the differences in the properties in the direction of forming and across. In perticular, the ductility properties viz. reduction in area, which is affected significantly. Whereas the casting has no anisotrophy at all, forging is a prisoner to this effect. This level of anisotrophy is dependent on the type and the level of impurity, the extent of working.
If one has to deal with HIC resistance, if the product is a casting there is cosiderable less problem, than what is called for a wrought product.
Regards,
MRCN
A similar question was answered in
Advantages of forging and casting over extrusion
thread367-44636
There, I essentially agreed with the answers above by EnglishMuffin on the forged grain structure being superior for applied stresses, and by mdighe on the segregation problem of castings. Although priyasachin claims that castings are isotropic, this is never entirely true since it takes a finite time for the heat of solidification to flow somewhere. Consequently, grain growth and segregation occur. Non-anisotropy isn’t necessarily a benefit either: in a functionally shaped forging, the grain structure becomes aligned to optimally resist applied loads. And, in castings, reinforcing ribs are generally anisotropic per design.
Advantages of forging and casting over extrusion
thread367-44636
There, I essentially agreed with the answers above by EnglishMuffin on the forged grain structure being superior for applied stresses, and by mdighe on the segregation problem of castings. Although priyasachin claims that castings are isotropic, this is never entirely true since it takes a finite time for the heat of solidification to flow somewhere. Consequently, grain growth and segregation occur. Non-anisotropy isn’t necessarily a benefit either: in a functionally shaped forging, the grain structure becomes aligned to optimally resist applied loads. And, in castings, reinforcing ribs are generally anisotropic per design.
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